The 4-hydroxy-benzoic acid long chain ester has a structure having a hydroxyl group and a hydrophobic group. On the basis of the structural feature thereof, the uses for a plasticizing agent, a compatibilizing agent, a surface active agent, and the like have been proposed.
As to esterification of a compound, a production process of an ester in which a carboxylic acid and an alcohol as the raw materials are reacted in the presence of a protic acid catalyst such as sulfuric acid; the catalyst and the unreacted carboxylic acid are removed from the resulting reaction liquid; and, if necessary, purification such as crystallization or distillation is conducted is known (Patent Document 1).
As to also esterification of 4-hydroxy-benzoic acid, it is known that a 4-hydroxy-benzoic acid short chain ester is relatively easily obtained by a reaction of 4-hydroxy-benzoic acid with a short chain alcohol having 1 to 6 carbon atom(s).
In a reaction of 4-hydroxy-benzoic acid with a long chain alcohol having 16 or more carbon atoms to obtain a 4-hydroxy-benzoic acid long chain ester, when the acid and the alcohol are similarly reacted in the presence of a protic acid catalyst, however, the generation of a side product such as an ether generated by dimerization of the long chain alcohol and a sulfate ester generated by a reaction of the long chain alcohol with the protic acid catalyst is inevitable.
The side products have physical properties similar to those of the 4-hydroxy-benzoic acid long chain ester which is the target substance, and are therefore difficult to be removed using crystallization or distilling. Therefore, no 4-hydroxy-benzoic acid long chain ester of high purity can be obtained.
When the scale increases, in general, the reactivity is degraded and the yield of the target substance is reduced. Therefore, a production process in which a 4-hydroxy-benzoic acid long chain ester can be obtained at a substantially equal yield even when the scale increases has been sought.
On the other hand, purification is generally conducted by extraction using water or alkali water after melting a crude crystal which ordinarily includes the target substance or after dilution using a non-aqueous solvent. As to a crude composition of the 4-hydroxy-benzoic acid long chain ester containing impurities such as the unreacted carboxylic acid and the catalyst, however, even when extraction is attempted by adding water or alkali water, the extraction is difficult because the liquid separation property thereof is extremely low. Even when the extraction is conducted, the yield and the purity are low and no target substance of high purity can be obtained.
Patent Document 1: Japanese Patent Publication No. 2014-108928